The present invention relates to a process and an apparatus for the continuous measurement of element contents in slurries independently of slurry density and slurry composition, by use of the X-ray fluorescence analysis method (XRFA).
Due to the rising worldwide need for raw materials, it is increasingly necessary nowadays to mine deposits with a low content of the desired raw material. Such deposits are primarily exploited with the use of the flotation method, wherein the desired, valuable mineral is obtained from an aerated suspension of finely ground raw minerals and water, a so-called flotation slurry, with the aid of chemicals. To be able to operate facilities using this method, frequently with widely branched-out slurry conduits, in an economical manner, a continuous analysis of the product streams is of decisive importance. Therefore, analytical devices are required which, with maximum speed, indicate the mineral contents of interest at strategically important points in the process and thereby make it possible to quickly intervene in the operation of the process. This is necessary, in particular, when monitoring the waste streams and the concentrate streams leaving the production facility. Losses of valuable minerals in the waste stream mean considerable financial setbacks in the operation of such a facility.
Further, the quality requirements posed by the processing industry using the resultant concentrates are currently very high and can be met only with difficulty. Only a rapid, continuous quality control affords the possibility to extensively preclude impaired production by a controlled intervention in the process operation. The posed requirements not only relate to providing concentrates with a specific content of valuable mineral, but also to providing the concentrates with precise proportional values for so-called deleterious components. Exceeding such proportional values can lead to considerable financial losses and/or to a discarding of the entire product.
It is even currently still quite customary, especially in relatively small flotation plants, to conduct the control of the process streams by means of wet chemical analysis. These analysis methods cannot be effected continuously and require a considerable amount of time. It is initially necessary, using wet analysis, to withdraw samples from the product streams and to process these samples appropriately (drying, grinding, homogenizing, etc.) before analysis can begin. In such wet chemical analysis methods, a time delay of several hours, even up to a day, can be expected from the taking of the sample to the result of analysis. This can mean that entire daily productions will have to be discarded.
Time-consuming wet chemical analysis is, in part, being replaced by X-ray fluorescence analysis. In this method, use is made of dispersive, conventional multichannel X-ray spectrometers with excitation by an X-ray tube. To their disadvantage, use of these devices involves a time delay between the taking of the sample and the analytical result, caused by the necessary preparation of the sample, even though a substantial saving in time is obtained as compared with wet chemical analysis.
In order to reduce the time delay occurring with these processes between the taking of the sample and the analytical result, devices and processes have been developed making it possible to carry out a direct analysis at the product stream. In this context, mention can be made of the on-stream analysis system Courier 300 developed by the company Outokumpu Oy of Finland. This device is, in principle, a continuously operating sample-taking system with discontinuous analysis based on X-ray fluorescence. In this process, a partial product stream is conducted from various sample-taking points in the flotation plant, via pumps and pipelines, to a battery of measuring cells. A movable measuring head with X-ray tube and analytical section travels at predetermined time intervals along the various cells and thus determines, in a quasi-continuous fashion, the elemental contents of the individual slurry streams. Since this arrangement is very expensive, it can hardly be considered for use in relatively small flotation plants.
So-called immersion probes have also been developed. In contrast to the conventional X-ray fluorescence method, these devices utilize, in place of excitation by an X-ray tube, excitation by an isotope source. The immersion probes are hung in the slurry stream, and in case of flotation plants, for example, in the so-called flotation cells. One disadvantage here is the inhomogeneity of the slurry usual in flotation cells. Further, an additional density measuring probe is necessary in all cases. Such immersion probes have been developed by the companies Outokumpu Oy of Finland, Philips of Australia, and NUTMAQ of England.
All of the on-line analysis devices heretofore developed on the basis of X-ray fluorescence initially determine the element content of the slurry. The determination of the element content in the solid matter is possible only by means of an additionally required measurement of the slurry density. Since densimeters, however, operate precisely only in a bicomponent system of liquid/solid matter, the results can be greatly falsified, for example, by air occlusions in the slurry, which can be expected in flotation processes. This fact must be considered a decisive disadvantage of the conventional XRFA processes.
In addition to the devices operating on the basis of X-ray fluorescence, attention must also be drawn to on-line analysis devices operating according to the principle of neutron activation analysis. In these devices, a partial slurry stream flows continuously first through an irradiation cell with the neutron source. Here the slurry is "activated" and then flows via an inductive flowmeter into a measuring cell provided with a detector, where the induced activity is measured. During backflow, the slurry passes a densimeter. Thus, neutron activation analysis devices absolutely require a density measurement. Furthermore, a specific slurry throughflow, constant at all times, must be maintained.